Underground storage and method of forming the same



March 26, 1968 c. r. BRANDT UNDERGROUND STORAGE AND METHOD OF FORMING THE SAME Filed June 10, 1964 2 Sheets-Sheet 1 FRACTURE FLUID e 0 Q 9 O o 0 0 a o d a 0 O o oooacoooo oooocoooo 0000000 ooooocac 00000 0900470066 BLANKET FLUID 9 TO DISPOSAL 5 SOLVENT 6 O O a O eue IN VEN TOR.

T. BRANDT BY ZZWM ATTORNEY March 26, 1968 c. T. BRANDT 3,374,633

UNDERGROUND STORAGE AND METHOD OF FORMING THE SAME Filed June 10, 1964 2 Sheets-Sheet 2 A55 4 NON SOLVENT e 65 JNVENTOR.

CARL T. BRANDT QMZZYQJL ATTORNEY United States Patent Office 3,374,633 Patented Mar. 26, 1968 3,374,633 UNDERGROUND STORAGE AND METHOD OF FORMING THE SAME (Iarl T. Brandt, Tulsa, Okla, assignor to Continental Oil Company, Ponca City, Okla., a corporation of Delaware Filed June 10, 1964, Set. No. 374,060 16 Claims. (Cl. 61'--.5)

The present invention relates generally to underground storage and, in one aspect, the present invention relates to methods of forming subterranean storage caverns utilizing solution mining techniques and the cavity thus formed and to methods and apparatus for removing product from the caverns thus formed.

Within the last few years, increasing attention has been given to the problem of storing fluids and, in particular, of hydrocarbon and cryogenic fluids. In the several years previous to the present era, most commonly such fluids were stored in above-ground tanks which necessitated, in the case of cryogenic fluids, the utilization of extensive thermal insulation. Not only have such storage facilities proved to be unwieldy due to the requirement for structural integrity in the storage container itself, but the problems wrought by the vulnerability of above-ground storage have proved such schemes to he imperfect at best.

While below-ground storage has been found by the industry to achieve many desirable results not characteristic of the above-ground counterpart, nevertheless, such belowground storage has also been found to have attendant problems. Not the least of these problems lies in the difliculty which has been encountered in exactly predicting the size, extent and even location of underground caverns when such caverns are formed by solution mining techniques. Heretofore it has not been uncommon to find that portions of stored materials are lost for recovery due to several factors. For instance, when prior art techniques are employed to form storage caverns, the vertical and lateral extent of such chambers has not always proved controllable due to the relatively indiscriminate nature of the solvent action. Moreover, irregularities in the roof of the chambers commonly entrap substantial quantities of stored materials which cannot be subsequently removed by prior art methods.

It is, therefore an object of the present invention to suggest methods for controlling the extent and placement of a subterranean storage cavity.

Another object of the present invention is to suggest a method for forming a subterranean storage cavity without attendant ancillary fracture fissures. I

Still another object of the present invention is to suggest methods for controlling the placement of a cavity beneath the ground and for controlling the nature and extent of the top of the cavity.

Yet another object of the present invention is to suggest a method for maintaining a nonsolvent blanket on portions of a soluble subterranean bed during the forming of a cavity in the bed by solution.

Still another object of the present invention isto suggest methods for forming a subterranean storage cavity without the necessity for casing bore holes within the formation.

Still another object of the present invention is to suggest methods for forming underground storage cavities from which stored material may be easily removed wit-hout regard to the depth of material within such cavities.

Another object of the present invention is to suggest methods for quickly and economically forming storage cavities of an improved character.

Still another object of the present invention is to suggest methods for recovering stored product from a storage cavern.

An additional object of the present invention is to suggest methods for forming underground storage cavities in thin-bedded soluble salt deposits.

Still another object of the present invention is to suggest apparatus for removing completely product stored in underground caverns.

Other objects of the present invention will appear to those skilled in the art as the following description of this invention is read.

In one aspect, the present invention may be summarized as a method for forming of an underground storage cavity wherein a plurality of bore holes are drilled into a soluble underground formation at least to a point near the bottom of the formation. At least one of the holes is then cased to a point adjacent the top of the formation and a packer is set in the lower open hole slightly above the point at which it is desired to start a solution operation. Suitable apparatus is then employed to notch the soluble formation slightly below the packer and subsequently sufficient hydraulic pressure, utilizing a nonsolvent liquid, is placed against the notch to start a fracture toward the second bore hole. Ultimately, the fracture is extended, utilizing a nonsolvent liquid, to communicate with each of the bore holes. A solvent fluid is then passed through the fracture so created to form a solution channel after which the cavity is itself formed by solvent washing.

In one embodiment of the present invention, a vertical chamber may be formed around at-least one of the bore holes for holding a quantity of nonsolvent blanket material which has a lighter specific gravIty than does the solvent utilized to form the cavity.

In an additional aspect of this invention a floating string is provided within at least one bore hole, with the end of said string located near the top of a storage cavity. Means are provided at the upper portion of said string to place said string selectively into communication with a product header and a source of nonsolvent material lighter than the product stored within the chamber. A wash string is likewise provided within a bore hole intersecting the cavity, and the lower end of this wash string is located near the bottom thereof. Means are provided at the upper portion of said wash string for placing said string selectively into communication with a product header and a source of nonsolvent material heavier than the product stored within the chamber.

A fuller understanding of the present invention may be garnered from a perusal of the following specification when read in conjunction with the drawings wherein:

FIGURE 1 is a schematic cross section of a portion of the earth showing a soluble underground formation and appurtenant cavity forming equipment as it appears when an initial solution channel has been formed between two bore holes;

FIGURE 2 is a cross section similar to that shown in FIGURE 1 showing the subterranean formation after substantial amounts of solvent have been circulated through the solution channel;

FIGURE 3 is a schematic cross section similar to that shown in FIGURES 1 and 2 which shows the configuration of an underground storage cavity at the termination of a solutioning process;

FIGURE 4 is an enlarged, fragmentary cross-sectional view showing the relationship of elements in one of the bore holes shown in FIGURE 2 at the time construction of a vertical storage cavity for blanket material is begun; and

FIGURE 5 is a cross-sectional view similar to that shown in FIGURE 4 wherein the final configuration of the vertical blanket material reservoir is delineated.

Turning now to the drawings and in particular to FIGURE 1, there is shown a relatively soluble subterranean formation 11 which, in the embodiment shown,

includes stringer or lenses of relatively insoluble material, such as shale stringers 12. The soluble formation may include any of several different materials commonly found underground, such as sodium chloride, sodium nitrate, potassium chloride, the alkaline earth metal salts, such as Epsom salt, kiersite, calcium chloride and the like, or many of the water soluble minerals, such as kainite, sylvanite, carnallite, etc. Commonly halite beds are encountered and these have been found to be suitable for the formation of subterranean storage cavities.

As a first step in the formation of the desired cavity, a pair of bore holes a and 10b are drilled into formation 11 at least to the depth at which it is desired to place the bottom of the resulting cavity. During the construction of these bore holes, either a solvent or nonsolvent drilling fluid may be utilized for the initial portion of the drilling. However, when the drilling reaches a point at or near the top of soluble bed 11, drilling is interrupted and a casing 13 is cemented into place into each of the bore holes. Subsequently, the holes are extended into soluble formation 11 utilizing a nonsolvent drilling fluid. As used herein, the term nonsolvent drilling fluid indicates any fluid which will not substantially dissolve the material of bed 11. Any number of suitable materials may beutilized for this purpose, such as liquid hydrocarbons, including diesel oil, kerosene and similar materials. Ordinarily, however, it will be found advantageous to use an aqueous solution which is substantially fully saturated under conditions of pressure and temperature existing in the formation with the material from which bed 11 is made up. It has been found that when the nonsolvent drilling fluid is utilized, a uniform hole in the soluble formation can be formed which has relatively parallel sides. Because of the uniform, parallel walls of the hole thus formed, open hole packers may be used in the subsequent fracturing step;

After extension of the bore holes to the desired depth, the extended portions are preferably not cased but are left open hole as shown in FIGURE 1. For an understanding of the reason for leaving these portions of the holes uncased, it is necessary to consider the later utilization of the cavity. More particularly, after a cavity is formed by this process, it is then filled with the material which is to be stored. Subsequently, when it is desired to remove this material, quite commonly a fluid immiscible with and more dense than the stored material is forced into the cavity with resulting ejection of the stored fluid from one of the bore holes. When open holes are utilized, as contradistinguished with cased holes, it is then possible to place an outlet for the stored fluid or the displacing media at substantially any vertical position within the cavity, depending on the needs of the situation. On the other hand, if the holes are cased to the bottom of the cavity and a heavier immiscible re- 7 covery fluid is injected, the heavier fluid remains on the bottom of the cavity and thus traps the lighter stored product between the end of the recovery pipe and the roof of the cavity. Manifestly, this type of shortcoming does not characterize open hole structures.

When the holes are thus completed, suitable perforating or notching apparatus, such as a gun perforator, not shown, is then placed in the hole opposite a point in formation 11 at which it is'desired to form a solution channel between bore holes 10a and 10b. Upon activa-.

nonsolvent fracturing fluid. The interior of reservoir 17 communicates with a pump 18 through a valve-12 and from thence with a wash string 21 shown suspended in hole 10a wherein an open hole packer 22 is located immediately superjacent radial notch 14. In addition, a suitable reservoir 24 for solvent material is provided on the surface of the ground in communication with pump 18 through a line 25 having a valve 26 therein.

After packer 22 has been positioned as shown in FIG- URE l, valve 19 is opened and valve 26 is closed after which pump 18 is actuated to draw fracturing fluid from reservoir 17, through valve 19 and down wash string 21 to place the nonsolvent fracturing fluid opposite notch 14 at sufficient pressure to raise the overburden and create a radial fracture 23 extending from hole 10a. After the initial portion of fracture 23 has been formed, additional nonsolvent fluid is pumped into the formation to extend the fracture until bore holes 10a and 10b are in communication with each other through formation 11 by means of the fracture. This extension may be achieved by continuing the fracturing process in hole 10a or, should it be desired, notching and fracturing may be initiated from bore hole 1012 so that two intersecting fractures meet within formation 11 somewhere between bore holes 10a and 10b. a

In carrying out the fracturing step of this process, pres sures which may be utilized correspond to pressures which have been utilized in ordinary oil Well fracturingtech breakdown pressure. Because of these and other variables, it is not possible to establish generally suitable pressure ranges which can be expected to fit all possible subterranean conditions. However, in spite of the impossibility of establishing fracture pressures prior to actual.

practice, those skilled in the fracturing art will have little difficulty in completing the desired fracture since, as was stated earlier, the mechanism of the fracturing step will be quite well understood from oil well fracturing experience.

It is stressed that the fluid which is used for the fracturing step is a nonsolvent with regard to the soluble,

portion of formation 11 and, as such, it may be any of the fluids mentioned previously forthe nonsolvent drilling fluid. As in the case of the drilling fluid, it is preferred to use an aqueous solution which is substantially completely saturated with the salt or salts of which soluble formation 11 is made. 7

It will be noted that radial fracture 23 will extend on both sides of bore hole 10a. When a nonsolvent fracturing fluid is used, the portion of the fracture not between bore holes 10a and 10b is healed upon reduction of the opening around hole 10a. On the other hand, when solvent type fracturing fluids are used under these circumstance, there is a tendency for material to be leached from the area of the fracture between bore holes 10a and 10b and also from the other portions of the radial fracture. Because of the removal of this material in an indiscriminate manner, subsequent release of pressure along the fracture may not result in the desired healing but instead an opening will remain, which opening tends to be enlarged upon subsequent dissolving of the for mation. When this occurs, uncontrolled and, to a large extent unknown extensions of the cavity are formed which can result in loss of portions of the material which is later stored therein, or in mixing of such material with other material stored in adjacent cavities."

When fracture 23 is completed between holes 10a and 10b, pressure is maintained on the fracture while v'aive 19 is closed and valve 26 opened, whereupon a suitable solvent material from reservoir 24 is drawn through valve 26 by pump 18, and from thence down through wash string 21, past packer 22, and into the portion of fracture 23 lying between bore holes a and 1%. Continued circulation of the solvent material results in the formation of a solution channel 27 between the two bore holes. Simultaneously with the injection of solvent in bore hole 10a, fluid is withdrawn from the formation through valved discharge line 29 located in bore hole 101:. As soon as a definite solution channel 27 has been formed, the pressure on the formation is released whereupon the portions of fracture 23 not lying in the solution channel close and heal, thus preventing unwanted extensions of the subsequently formed cavity along the fracture line.

If desired, the nonsolvent fracturing fluid may have incorporated therein propping agents, such as sand particles and the like which are Well known in the fracturing art. When such propping agents are utilized, it is then unnecessary to keep suflicient pressure on the radial notch 14 to hold the fracture open during initial solvent circulation to form solution channel 27.

It may also be found desirable to form solution channel 27 by circulation of fluid in two directions. For instance, solvent may be circulated -first from bore hole 10a to 1012 and subsequently from 10b to 10:1. Should this type of procedure be desired, it will of course be necessary to equip bore hole 101) with the same well head elements shown in connection with bore hole ltla. For clarity, however, the additional valving and piping necessary for such equipping is not disclosed in FIG- URE 1.

After solution channel 27 is formed, it is then necessary to circulate additional solvent through the channel in order to form and enlarge the desired storage cavity. At the time this solvent material enters the channel from one of the bore holes, it contains little or no dissolved solids. However, as it passes from the inlet to the outlet of the solution channel, more and more solids are dissolved therein with the result that the rate of solution adjacent the inlet of channel 27 is higher than is the rate of solution adjacent the outlet. The result of this situation is the formation of an unsymmetric cavity which is large near the inlet and which tapers toward the outlet. At least two remedies may be employed in order to overcome this tendency to form an unsymmetric cavity and to create one which is substantially symmetrical. First, a blanket of nonsolvent material may be maintained between the formation and those portions of the cavity roof which are a predetermined height so that further solution action in these areas is precluded. Second, circulation of solvent betwen holes may be reversed in order to introduce fresh solvent into the previous discharge bore hole. In a preferred embodiment of the present invention, blanket material is utilized in combination with a reverse circulation process. When these two independent techniques are thus used together, the chances for obtaining a symmetric cavity having a roof at a controlled, predetermined elevation are optimized.

In order to insure the presence of blanket material in those portions of the cavity which have reached a desired height, it is, of course, necessary to provide some means for constantly supplying such material to each portion of the cavity as it reaches this height. As a feature of the present invention, it has been discovered that unexpectedly good results may be obtained in the maintenance of the blanket material by the formation and utilization of a vertical blanket material reservoir around the lower portion of at least one of the bore holes. An understanding of one method for forming such a reservoir, indicated generally at 31, may be obtained from an examination of FIGURES 2, 4 and 5 in conjunction with the following discussion.

As a first step in the preparation of the desired vertical reservoir, wash string 21, together with its associated packer 22, is removed from bore hole 10a and a floating string 32 is placed in the bore hole with its lower end located at a point from about one to six feet below the lower terminus of casing 13. A second wash string 33 is subsequently placed within floating string 32 in such a manner that the lower terminus of the wash string lies at a point near (within about one to ten feet, depending on the height of the cavity) the bottom of the proposed cavity. It might be noted that the presence of wash string 33 during construction of vertical reservoir 31 is not absolutely necessary. However, it should, as a matter of operating efliciency, be installed at this time. Additionally, identical wash and floating strings are shown in bores holes 10a and 10b although it is to be understood that it is not absolutely necessary to form vertical reservoirs surrounding both bore holes, although it is preferred to do so.

The surface equipment with which the tool strings communicate comprises a reservoir 36 for blanket fluid and a pump 35 which communicates with the interior of casings 13 through a bifurcated line 37 having a valve 38 in each arm of the bifurcation. Also in communication with the interior of each casing 13 is a line 39 having a valve 41 therein which communicates with a common header line 42. A centrally located solvent reservoir 43 is provided in communication with a central pump 44 which operates through header lines 42 or, alternately, through a disposal line 46 depending upon the position of four valves 47, 48, 49' and 50. Bifurcated line 37 also communicates with the interior of each of the floating strings 32 through a valve 52 and with the interior of each of the wash strings 33 through a valve 53. Similarly, each header line 42 communicates with the interior of a floating string 33 through a valve 53 and with the interior of a wash string 33 through a valve 54.

With a floating string 32 installed as shown in FIG- URES 4 and 5, solvent material, preferably water, is circulated from reservoir 43 through pump 44, valve 48, lines 42 and 39 and valve 41 into the annular space between casing 13 and floating string 32. This material initially follows the flow lines indicated in FIGURE 4, while in the latter stage of development of the reservoir it follows the flow lines indicated in FIGURE 5. When the solvent material reaches the bottom of the bore hole, it then passes through solution channel 27 and is ultimately forced through wash strings 33 in the other bore hole and from thence through valve 54, line 42 and valve 49 to disposal line 46. As circulation of solvent is continued, eddy currents are set up as indicated by numeral 40 at points around insoluble beds 12, which results in the enlarging of vertical reservoir 31 in a lateral direction below each of the insoluble beds 12. After reservoir 31 has been completed to the stage shown in FIGURE 5, circulation of solvent in the annular space between casing 13 and floating string 32 is discontinued.

At the completion of a vertical reservoir as described above, valve 38 is opened and nonsolvent blanket material 34, having a specific gravity less than the specific gravity of the solvent, is pumped from reservoir 36 down through the annular space between casing 13 and floating string 32. Injection of this material is continued until returns of thematerial are obtained from the bottom of floating string 32 indicating that reservoir 31 above the bottom of the floating string is filled with the blanket material. At this time further injection of blanket material is discontinued and the formation is now ready for further solvent action in the development of the cavity itself.

During the development of the cavity indicated generally by numeral 56, a suitable solvent is pumped from reservoir 43, through the related valves, and down into hole 10a through either wash string 33 or floating string 32. Subsequently, the solvent flows through solution channel 27 and is ultimately removed through bore hole b, by wash string 33. As circulation is continued, a relatively large chamber develops immediately adjacent hole 10a and this chamber tapers, becoming smaller and smaller toward hole 10b. As the portion of the hole immediately adjacent hole 10a reaches the level as indicated in FIGURE 2, blanket material 34 spreads out from vertical reservoir 31 around bore hole 10a to place a nonsolvent insulating blanket between the solvent acting within the cavity and the top of the chamber adjacent the hole.

After solvent circulation has been continued a sufficient length of time to allow formation of a substantial cavity adjacent hole 10a, circulation of solvent is reversed and solvent is then injected in hole 1% and removed from hole 10a in the manner described above. Assuming that a vertical reservoir 31 has been formed around hole 10b as shown in FIGURE 2, then as the reverse circulation transpires, a nonsolvent insulating blanket spreads around the top portion of the cavity immediately adjacent hole 10b in a manner similar to that described in the earlier discussion of hole 10a. Moreover, as this reverse circulation progresses, a larger and larger chamber is formed around hole 10b with a resulting cavity.56 similar to that shown in FIGURE 2.

As further dissolution takes place around the bore holes, cavern 56 is enlarged to the level of the ends of floating strings 32 whereupon the blanket material spreads out from reservoir 31 and floats upon the surface of the solvent within the cavity to cause lateral solutioning, and the cavity 56 eventually achieves the shape shown in FIGURE 3. Before this transpires, however, it is necessary to refill vertical chamber 31 several times in order to make available sufficient blanket material to' completely cover the top of cavity 56 as shown in FIGURE 3. Moreover, it will be desirable to reverse solution circulation from time to time to insure a symmetrical cavity.

It will be noted in FIGURES 2 and 3 that as the formation of the cavity progresses, more and more insoluble residue is deposited on the bottom of the cavity. However, since =both holes 10a and 10b are uncased, the presence of this residue does not unduly handicap subsequent utilization of the cavity for storage purposes. On completion of the cavity, wash strings 33 are raised to a point just clear of the debris in the bottom of the cavern.

Prior to filling cavity 56, the annular space between wash string 33 and floating string 32, and the space between casing 13 and floating string 32, and the interior of wash string 33, are connected to a product header 57 by means of valved lines 58, 59 and 60, respectively (FIGURE 3). In addition, a flow line 61 for displacement media A which is heavier than the stored product is placed in communication with the interior of wash strings 33 by means of a line 62 having a pair of valves 63 therein. The annular space between casing 13 and floating string 32 is also connected to line 64 through valves 65 so that displacement media B which is lighter than the stored product may be introduced into the top of the cavern. It will be noted that in FIGURE 3, this equipment is shown as being duplicated at each bore hole; however, such duplication is not absolutely necessary but is ordinarily provided for convenience in filling and recovering product from cavity 56.

When it is desired to place product in cavity 56, valved line 58 is opened and product flowed from a source not shown through header 57 and line 58 into the annular space between casing 13 and floating string 32 and from thence into cavity 56. In the event that nonsolvent fluid is present in the cavity, it is withdrawn through wash string 33 simultaneously with the injection of product into the cavity. Ordinarily when nonsolvent is withdrawn during admission of product into the cavity such withdrawal will take place in the wash string located in the bore hole opposite the bore hole through which product is injected to the cavity.

When it is desired to remove product from the cavity,

a nonsolvent fluid is transmitted from a source not shown through flow line 61 past at least one of the valves 63 and into the interior of wash string 33. This nonsolvent is characterized by being unreactive with the formation material, and further characterized by being heavier than, unreactive with, and immiscible with the stored product. Commonly, saturated brine will be used for this purpose. The heavier nonsolvent, designated previously as nonsolvent A, then passes downwardly through wash string 33 and empties into the bottom of cavity 56. Because the stored product is lighter than nonsolvent A it will, of course, float on top of the nonsolvent and is removed through floating string 32 and line 59 into header 57 and ultimately into a product supply line, not shown. Alternately product may be recovered through casing 13, valved line 58 and header 57.

In spite of precautions to insure a uniform top for cavity 56, it is not uncommon for recesses to be formed within the top of the cavity due to uncontrolled caving and the like. When nonsolvent A is used as the recovery fluid, these irregular depressions entrap product and prevent its being removed through either casing 13 or floating string 32. In order to remove materials from these irregular depressions which may be formed on the top of cavity 56, it has been found that a nonsolvent material B which is lighter than the stored product may be injected into cavity 56 through the annular space between casing 13 and floating string 32 while product is withdrawn through at least one of wash strings 32. A variety of ma terials may be used as the nonsolvent B and the choice of this material depends to some extent upon the nature of the product which is stored within the cavity. Most commonly, nonsolvent B will be material which is ordinarily in the gas phase under reservoir conditions. Moreover, because of the explosive nature of LPG which is commonly the product stored, nonsolvent B will be not only unreactive with the material of the formation but also will a are removed through floating string 32. In a less desirable alternate arrangement, nonsolvent B is injected until the surface of the product reaches the lower end of floating strings 33.

Example To aid in a better understanding of certain aspects of the present invention, a specific example of one method by which the invention may be practiced is hereinafter presented. For ease in reference, the specific example will be referred to in the drawings; however, it is to be understood that the specific arrangement of components detailed in the drawings is not necessary for the practice of the invention.

In the north central portion of Oklahoma near the town of 'Medford, the Wellington formation contains a salt section, the top of which lies at approximately 812 feet from the surface of the earth and which is approximately a 116 feet thick. This salt section is comprised of interlayered dirty salt and shale stringers which are from ap-- proximately three to about ten feet in thickness. A pair of bore holes 10a and 10b are drilled to the bottom of the salt formation at a distance apart of approximately 400 feet. In drilling these wells ordinary aqueous drilling mud is utilized until the top of the formation is reached, whereupon casing is set and cemented. Subsequently, a sodium chloride saturated brine is utilized as a drilling mud for extending the wells from the top to the bottom of the formation. After the wells have been drilled, a wash string is placed in bore hole a and an open hole packer is set at the bottom of the wash string. Similarly, a discharge line 29 is suspended in hole 10b with the lower terminus of the discharge line being approximately level with the lower terminus of the wash string 21. Subsequently, pump 18 is actuated and sodium chloride saturated brine is placed opposite the face of the lower bore hole underneath the open hole packer. Brine pressure is increased until it reaches approximately 1300 pounds per square inch gage on the face of the formation whereupon the formation ruptures, as evidenced by an abrupt decline in pressure at the Well head. Operation of pump 18 is continued at a rate of 29 barrels per minute and at a pressure of approximately 2650 p.s.i.g. until returns of brine are obtained through discharge line 29. Thereupon valve 19 is closed and valve 26 is opened while maintaining pressure on the formation at approximately 1235 p.s.i.g. and circulation of unsaturated water is continued at a rate of 1175 gallons per minute for approximately 3.0 hours to open up a solution channel, shown in FIGURE 1 as channel 27. After the water has been circulated for 3.0 hours, circulation is terminated and the packer and wash string are removed from hole 10a while the discharge line is removed from hole 1%. Subsequently, a floating string and wash string are placed in each of the holes as shown in FIGURE 2 whereupon unsaturated water is pumped into hole 10a in the annular space between the casing and the floating string. Pumping of the water is continued at a rate of 160 gallons per minute with simultaneous removal of the water through the wash string in hole 10b at the same rate. After circulation has been continued for approximately 8.0 hours, injection of unsaturated water in hole 10a is terminated and water circulation is initiated between the casing and floating string in hole 10b at a rate of 160 gallons per minute while the water solvent is simultaneously removed through the wash string located in hole 10a. Injection of water into hole 1012 at this rate is continued for a period of approximately 8.0 hours. At the end of this time, injection of water is terminated whereupon a vertical reservoir chamber, such as shown in FIGURE 5, is located at the lower end of each of the bore holes.

Each of the vertical blanket material reservoirs is then filled by injecting blanket material, in this case kerosene, into the annular space between the casing and floating string. Injection of the kerosene is carried out at a rate of approximately gallons per minute with simultaneous withdrawal of fluid through the floating string at the same rate. Injection of kerosene is continued until returns of this material are noted in the fluid being withdrawn through the floating string. At this point, injection of kerosene is terminated.

Solution removal of the material within the proposed cavity area is now begun. Initially, unsaturated water is passed downwardly through the wash string in hole 10a at a rate of 50 gallons per minute and at a well head pressure of 100 psi. gage. Simultaneously fluid is withdrawn through the wash string located in hole 1% at the same rate. Injection of water is continued for a period of approximately 72 hours at the end of which time injection in hole 10a is terminated. Subsequently, water is injected in the wash string in hole 10!) at a well head pressure of about 100 psi. gage and at a rate of 50 gallons per minute while fluid is withdrawn through the wash string is hole 10a at approximately the same rate. Such injection is continued for a period of approximately 72 hours whereupon injection is reversed between the wells. This process is continued for approximately 12 days with the injection and recovery wells being reversed about every 72 hours. Additionally, the kerosene within the vertical reservoirs is replenished periodically. In the present example such replenishment takes place after the first 48 hours of water injection and at the end of each 168 hour interval thereafter until the completion of the solution cavity. Such replenishment is accomplished in precisely the same manner as the initial filling of the vertical blanket chamber was initially accomplished, that is, kerosene is forced downwardly through the annular space between the casing and floating string while fluid is removed through the floating string. Injection of the kerosene is terminated upon receipt of return of kerosene in the fluid removed through the floating string.

After completion of the cavity as above-described, it is full of water with a layer of kerosene along the top. Subsequently, propane is pumped into the cavity through the wash string located in well bore 10a at a rate of approximately gallons per minute while water is withdrawn through the floating string in 101) at approximately the same rate. Injection of propane is continued at this rate until returns of propane are noted in the stream being removed through the floating string in hole 10b. At this time, injection of propane is discontinued.

When it is desired to remove the propane from the cavity, natural gas under a pressure of approximately 400 psi. gage is injected intothe floating string in hole 10a while fluid is removed through the floating string in hole 10b. At such time as returns of natural gas are noticed coming from the floating string in hole 10b injection of natural gas is terminated and water is then injected into the wash string in hole 10a at a rate of 200 gallons per minute. Simultaneously With the injection of water, propane is withdrawn through the floating string in hole 10!) at approximately the same rate. Such simultaneous injection of Water and withdrawal of propane is continued until returns of water are observed in the propane recovery line in hole 10b.

Pursuant to the requirements of the patent statutes, the principle of this invention has been explained and exemplified in a manner so that it can be readily practiced by those skilled in the art, such exemplification including what is considered to represent the best embodiment of the invention. However, it should be clearly understood that, within the scope of the appended claims, the invention may be practiced by those skilled in the art, and having the benefit of this disclosure, otherwise than as specifically described and exemplified herein.

What is claimed is:

1. The method of forming an underground cavity in a soluble formation using a first and a second bore hole which comprises the steps of:

contacting a portion of said formation adjacent said first bore hole with a fluid which is a nonsolvent for the material of the formation;

increasing the pressure of said nonsolvent fluid until said formation is fractured in the direction of said second bore hole;

continuing to inject a fluid which is a nonsolvent for the material of the formation into the formation to complete a fracture between said second and first bore holes;

circulating a fluid which is a solvent for the material of the formation between said bore holes through said fracture, whereby a portion of the formation adjacent the fracture is removed to form a chamber and removing said solvent containing material of the formation from one of said bore holes.

2. The method defined in claim 1 wherein said nonsolvent fluid comprises a solvent fluid saturated with sufficient dissolved material to render it nonsolvent.

3. The method defined in claim 2 further characterized in that prior to fracturing a notch is formed in the formation from said first bore hole in the area where the fracture is later made.

4. The method defined in claim 3 further characterized in that a quantity of a second nonsolvent material having. a lower specific gravity than said solvent fluid is injected into at least one of said bore holes'after circulation. of the first said nonsolvent fluid is begun and prior to completion of the cavity, said quantity being sutficient 1 1 V to insulate at least a potrion of the roof of said cavity from contact with said solvent.

5. The method defined in claim 2 wherein the pressure in said fracture is maintained at a sufficiently high level to hold the fracture open until at least a solution channel is formed between said bore holes.

6. The method of forming an underground cavity in a soluble formation, utilizing a first and a second bore hole, which comprises the steps of:

easing said first bore hole to a point adjacent the upper surface of said soluble formation;

notching the formation from said first bore hole at a point substantially below said casing;

setting a packer within the first bore hole at a point above the notch and below the casing; introducing a fluid which is a nonsolvent for the material of the formation to the formation adjacent the notch under suflicient pressure to fracture the formation in a direction toward the second bore hole;

introducing additional fluid which is a nonsolvent for the material of the formation to the formation under sufficient pressure to place the fracture in communication with the second bore hole;

circulating solvent through one of the bore holes,

through the fracture and out the other of said bore holes to form a solution channel adjacent the fracture; withdrawing said packer; passing a solvent for the material of the formation down the casing within the first bore hole, and withdrawing said solvent from the bore hole to form a vertical reservoir surrounding a portion of said first bore hole; positioning a tubing string in the first bore hole such that the lower end of the tubing string is positioned below the casing and above the level of the solution channel; 7

positioning a second fluid which is a nonsolvent for the material of the formation having a lower specific gravity than said solvent fluid in the vertical reservoir around the lower portion of said tubing string;

circulating additional said solvent through the solution channel to form said underground cavity between the first and the second bore holes; and removing solvent containing material of the formation from the 'bore hole remote from the injection bore hole. a

7. The method defined in claim 6 wherein the first said non-solvent fluid comprises the solvent fluid saturated with suflicient dissolved material to render it nonsolvent.

8. The method defined in claim 7 wherein said fracture is formed adjacent the lower surface of the soluble formation.

9. The method defined in claim 8 wherein the pressure in the fracture is maintained at a sutficiently high level to hold the fracture open until said solution channel is formed. 7

10. The method defined in claim 9 wherein the solvent is withdrawn from .the formation through the solution channel and the second bore hole while the vertical reservoir surrounding a portion of the first bore hole is being formed.

11. The method for forming an underground cavity in a soluble formation which comprises the steps of:

drilling a first bore hole to a point adjacent the upper surface of said formation;

casing said first bore hole;

drilling, with a drilling fluid which is a nonsolvent for the material of the formation, an extension of the bore hole at least to a point within the formation adjacent an interface between a portion of the formation and an insoluble bed;

' drilling a second bore hole through said interface at a point spaced from the first bore hole;

forming a notch in the formation at said interface adjacent said first bore hole;

setting a packer in the first bore hole below the casing and above the notch;

introducing a fluid which is a nonsolvent for the material of the formation to the formation adjacent the notch under sufficient pressure to fracture the formation between the notch and the second bore hole;

circulating a solvent for the material of the formation between the holes through the fracture while maintaining sufficient pressure on said solvent to keep the fracture open, whereby a solution channel is formed in the soluble formation adjacent the fracture;

withdrawing the packer;

circulating a solvent for the material of the formation down the first bore hole and withdrawing said solvent through the solution channel and the second bore hole; 3

positioning a tubing string in the first bore hole such that the lower end of the tubing string is positioned below the casing and above the solution channel;

placing a liquid which is a nonsolvent for the material of the formation having a lower specific gravity than said solvent fluid within the vertical reservoir between the bottom of the casing and the bottom of the tubing string; and

circulating additional solvent for the material of the formation through the solution channel to form said underground cavity between the first and the sec ond bore holes and removing solvent containing material of the formation from the bore hole remote from the bore hole wherein solvent is injected.

12. The method for forming an underground cavity in a soluble formation which comprises the steps of:

drilling a first bore hole into the upper portion of said soluble formation;

casing said bore hole;

extending said bore hole to a lower level within said formation;

drilling a second bore hole into the formation at a point spaced from said first bore hole;

forming a solution channel between said first and second bore holes;

suspending a floating tool string within said casing and said first bore hole, the lower end of said floating tool string being positioned at a point subjacent the lower end of said casing;

passing a solvent fluid for the material of the formation downwardly in said first bore hole in the annulus between said casing and said floating tool string; and simultaneously withdrawing fluid from said formation to form a vertical reservoir surrounding the lower portion of said bore hole between the lower end of said casing and the lower end of said floating tool string;

injecting a nonsolvent for the material of the formation as a blanket material said nonsolvent having a density less than the density of said solvent utilized in forming the cavity down through the annular space between said casing and said floating tool string;

discontinuing the injection of said nonsolvent material after the lower level of said nonsolvent material reaches the lower end of said floating tool string;

thereafter continuing circulation of said solvent material through said solution channel to complete the storage cavity and removing solvent containing the material of the formation from one of said bore holes. 13. An apparatus for storing and recovering product which comprises: I

(a) an underground cavern; (b) at least one bore hole intersecting said cavern and communicating with the surface of the ground; (c) a product header;

(d) a first tubing string within said bore hole, said string having its lower end adjacent the upper portion of said cavern and being of such diameter with relation to said bore hole to provide an annular space between said bore hole and said first tubing string;

(e) means communicating with the upper portion of said first tubing string for placing said string into and out of communication with said product header;

(f) a second tubing string within a bore hole, said second tubing string having its lower end adjacent the lower portion of said cavern;

(g) a source of nonsolvent material having a density greater than the density of the said product;

(h) means communicating with the upper portion of said second tubing string for selectively placing the interior of said string into and out of communication with said product header and said source of nonsolvent material defined in paragraph (g);

(i) a source of nonsolvent material having a density less than the density of said product; and

(j) means communicating with the upper portion of a bore hole for selectively placing the interior of said bore hole into and out of communication with said product header and said source of nonsolvent material defined in paragraph (i).

14. The apparatus defined in claim 13 wherein the the top of said cavern.

15. The apparatus defined in claim 14 wherein said first tubing string is within the cased bore hole.

16. The apparatus defined in claim 15 wherein said second tubing string is within said first tubing string, and further wherein said second tubing string is of sufiiciently small diameter to form an annular space between said two tubing string.

References Cited UNITED STATES PATENTS 2,584,605 2/1952 Merriam et a1. 16611 2,772,868 12/ 1956 Brandt.

2,787,455 4/ 1957 Knappen 61-.5 X 2,850,270 9/ 1958 Hanson.

2,861,428 11/1958 Hendrix 61.S 2,880,587 4/1959 Hendrix et a1. 61.5 2,986,007 5/1961 Shook 61.5 2,994,200 8/1961 Carpenter 61--.5 3,000,442 9/1961 Gambill 166-42.1 3,018,095 1/ 1962 Redlinger 2995 X 3,050,290 8/ 1962 Caldwell et al 299 5 X 3,086,760 4/ 1963 Bays 2994 EARL J. WITMER, Primary Examiner. 

1. THE METHOD OF FORMING AN UNDERGROUND CAVITY IN A SOLUBLE FORMATION USING A FIRST AND A SECOND BORE HOLE WHICH COMPRISES THE STEPS OF: CONTACTING A PORTION OF SAID FORMATION ADJACENT SAID FIRST BORE HOLE WITH A FLUID WHICH IS A NONSOLVENT FOR THE MATERIAL OF THE FORMATION; INCREASING THE PRESSURE OF SAID NONSOLVENT FLUID UNTIL SAID FORMATION IS FRACTURED IN THE DIRECTION OF SAID SECOND BORE HOLE; CONTINUING TO INJECT A FLUID WHICH IS A NONSOLVENT FOR THE MATERIAL OF THE FORMATION INTO THE FORMATION TO COMPLETE A FRACTURE BETWEEN SAID SECOND AND FIRST BORE HOLES; CIRCULATING A FLUID WHICH IS A SOLVENT FOR THE MATERIAL OF THE FORMATION BETWEEN SAID BORE HOLES THROUGH SAID FRACTURE, WHEREBY A PORTION OF THE FORMATION ADJACENT THE FRACTURE IS REMOVED TO FORM A CHAMBER AND REMOVING SAID SOLVENT CONTAINING MATERIAL OF THE FORMATION FROM ONE OF SAID BORE HOLES. 